The principal objectives of the total project are two-fold, first to elucidate the intra-nuclear organization and distribution of specific DNA molecules in the nuclei of normal and malignant mammalian cells as the cells change in metabolic activity and growth. This entails the study of the molecular properties of alternative states of chromatin. Secondly, we are investigating the problem of specific macromolecular associations of nuclear proteins with particular DNA sequences in the mammalian genome and the nature of such associations. Both of these objectives touch closely upon the larger problem of genome organization and the basic mechanisms of transcription control in normal and cancer cells. 1) Is there a phase relation between repetitive nucleotide sequences and the associated proteins in human or monkey cells? 2) Are altered states of chromatin activity associated with altered states of chromatin structure at the level of the nucleosome or the nucleosome subunits? We are also continuing studies on the subunit structure of mammalian mitotic chromosomes isolated under a variety of ionic conditions compared with extended chromosomes in interphase nuclei. We are also examining chromatin in which the thymidine of the associated DNA is substituted to varying degrees with 5-bromodeoxyuridine. These are two alternative states of chromatin which are readily accessible to study and we already accumulated a body of data pertinent to the molecular events bringing about these particular changes in chromatin state and cellular metabolic activity. BIBLIOGRAPHIC REFERENCES: Maio, J.J. and Schildkraut, C.L. (1977). Mammalian metaphase chromosomes. In Methods in Chromosomal Protein Research (G. Stein, J. Stein and L. Kleinsmith, eds.). Academic Press, New York, In press. Musich, P.R., Maio, J. and Brown, F.L. (1976) Repetitive DNA and the subunit structure of chromatin. J. Cell Biol. 70, 247a.